The present disclosure is directed to a method and apparatus for evaluating quality and productivity in an assembly line situation. It is particularly intended for use with electronic component assembly and will be described in that context, namely a situation where typical electronic components are mounted on a printed circuit board (PCB) and one or more such boards are assembled into a system typically placed on a chassis, connected with a wiring harness, and are packed and shipped representing as the output of the assembly line. A typical system such as a stereophonic receiver, computer or other electronic device is as simple as a few components or as complex as can be required, often over a thousand components. Whatever the range of complexity, the present disclosure describes a method and apparatus for evaluation of process, assembly and test operations both during and subsequent to production.
The present disclosure is particularly directed to a real time evaluation system which provides immediate indication of problems in the manufacture and assembly on a typical PCB. Real time determination of problems and difficulties in the manufacture of such devices is important. The real time analysis provides far greater assistance in the operation of an assembly line for stuffing typical components into a PCB, soldering the components, running board tests, assembling several boards into a system typically requiring a chassis and wiring harness, and executing the other steps necessary to make the finished product. Whether the device has fewer than ten components or more than 1,000 components, real time analysis of the defect data is extremely useful in improving the proficiency of the production operations. Heretofore, product inspection has typically been by visual input, compiled on data sheets representing score cards of defects, and the data sheets have been collected on a batch basis. In addition, some assembly lines will utilize an occasional automatic testing equipment (ATE) which tests a partially or totally completed PCB with a set of electrical tests. Such data is typically collected along with the hand written reports from one or more inspection stations and all the data is thereafter grouped for a time interval, perhaps a week or so, and the data is compiled into reports which are then diagnosed. However, even while data is being collected to obtain a meaningful statistical basis so that production changes can be made, product is made continuously, and to the extent that defects are likely in the production situation, then the number of product rejects simply accumulates. PCBs rejected typically are handled on a rework basis, although there are occasions where it is economical to simply scrap the rejects without attempting rework. Whatever the response, to the extent that error analysis is not implemented in real time, to that extent the cost of rejects becomes unacceptable.
Consider a relatively complex system where the historical rejection rate is 25%. It is possible in accordance with previous practice to accumulate data for manufacture of a large number of units, say 1,000 units, test the 1,000 units, determine the basis on which 250 units ought to be rejected, collect data regarding the 250 units and analyze that data with a view of making corrections to the manufacturing procedure. Statistical analysis normally suggests that after the collection of this set of data that certain specific difficulties exist which can be dealt with. Some causes for rejection may have a more random nature and be less susceptible to statistical analysis.
By implementing the apparatus and method of the present disclosure, an entirely different approach can be accomplished. First of all, data is collected on a real time basis and made available for real time analysis. The data is processed on a real time basis so that the number of units which are rejected is inevitably reduced. More importantly, the analysis of defect data gives rise to more prompt corrections. If changes in the assembly line are implemented promptly, the possibility of 100% acceptance of the production run is much more likely. In fact, with real time data furnished, one need not wait for an accumulation of data to obtain statistical analysis. In other words, while conventional wisdom suggests accumulating data over a long interval, the present disclosure surprisingly enables implementation of early changes, such early changes enabling complete rearrangement of the process and thereby enabling acceptance improvement, even approaching 100% acceptance. This is otherwise impossibly difficult but for the implementation of the present disclosure.
Details of the disclosed apparatus and procedure will become more readily apparent upon consideration of the below written specification in conjunction with the drawings affixed to the present disclosure. It will be understood that this disclosure is set forth in the context of a complex electronic device which requires one or more PCBs which are assembled into a chassis, and to that extent, the assembly line is represented in a generalized fashion for electronic equipment manufacture including mounting of components, clipping component leads, soldering multiple components simultaneously typically using a wave solder machine, and conducting many other operations that are typical for manufacture of a complex electronic device.